The present invention relates to briquets having a metallic iron content for use in the manufacture of iron and steel as well as the binder used in the making of such briquets and the method of agglomeration.
In the manufacture of iron and steel, it is customary to make certain additions to the melting furnace such as various metalliferous products in the form of alloys such as ferrosilicon. Ferrosilicon normally contains a substantial amount of carbon.
In the briquets of the present invention, metallized iron, silica and carbon form the composition of a briquet which is of high value for foundry practice and other iron and steelmaking uses. The briquet avoids the requirement for expensive ferrosilicon additions in the foundry or steelmaking practice in which it is used.
The invented briquet preferably employs metallized iron fines as the basic ingredient in its composition. Previously known briquets employ iron oxide fines. The presence of metallized fines reduces the energy requirement for melting the invented briquet over what is required in prior briquets. Since the iron fines are in the metallized condition, the energy normally required for reducing iron oxide to iron is not a requirement in any process utilizing the invented briquets as feed material.
It is also a theory to which we subscribe, but do not wish to be held, that the iron contained in the invented briquet acts as a catalyst during reduction of the silica contained therein in the melting of the briquet. Of course, since the iron in the briquet need not be reduced before melting, the energy requirement is reduced. Furthermore, the iron, having a high specific gravity with respect to the other components of the briquet, is responsible for imparting a high apparent density to the briquet. A high apparent density is critical to the previously mentioned application as it is directly related to the briquet thermal conductivity. That is, a briquet possessing a high thermal conductivity will be able to effectively transfer the required thermal energy necessary for initiating and completing the silica reduction reaction.
The mechanism of heat tranfer in a melter, such as a cupola, is by forced convection of hot gases flowing counter-current to the gravity fed charge, and also by radiation, both inter-particle, and to a lesser degree from the inside walls of the vessel to the charge. In the Merkert patent, silicon metal or high grade ferrosilicon is produced in an electric submerged arc furnace where a highly localized heat source is created by the arc. The electric arc generates the necessary thermal energy required for reduction of silica by resistance heating, both in the slag and to a greater extent in the liquid metal.
Forced convection plays a minor role in the transfer of thermal energy. Thus, while a dense compact and hence high thermal conductivity compact is not critical to the successful application of heat transfer by convection, it is advantageous, and thus a desirable improvement.
The closest known prior art patents include Pietsch U.S. Pat. No. 4,032,352, Rehder U.S. Pat. No. 4,179,283, Merkert U.S. Pat. No. 4,395,284, Querengasser et al U.S. Pat. No. 3,431,103, and Harrison U.S. Pat. No. 1,134,128.
Pietsch teaches a binder composition for agglomerating direct reduced iron fines in order to prevent reoxidation of the metallized iron contained therein. Pietsch does not include granulated silica in his briquet. Further, he does not include a carbonaceous reductant in the briquet for the purpose of reducing the silica. His pitch component is present for use as a binder. It is noted that water is an essential ingredient in all of the binder compositions claimed by Pietsch.
Rehder teaches the briquetting of metal oxides only and has no direct reduced iron in his briquet. He utilizes two sources of carbon, a high reactivity and a low reactivity carbon.
Merkert teaches a briquet in which iron and a binder are optional and are not essential ingredients. He prepares porous compacts for use as a feed material to an electric furnace, the material having a low apparent density, high internal porosity, and low thermal conductivity. Merkert states that up to about 15% of the silica weight can be iron particles. His product is used as charge material for making silicon or ferro-silicon. Merkert develops thermal energy from an electric arc, which requires electrode consumption. The present invention is a low cost, high-iron, ferrosilica briquet, which uses thermal energy from coal and coke, as opposed to Merkert's thermal energy from electricity.
Querengasser et al teach the production of ferro-silicon utilizing a briquet with iron contents only as high as 8%. This is substantially lower than the iron contents of the briquet products of the present invention.
Harrison teaches a ferro-silicon product which has from 53 to 54.5% silicon. He states that regular alloys have from 25 to 60% silicon, which is the equivalent of 38 to 66% silica (SiO.sub.2), which is substantially more silica than that present in the invented briquet product.
The present invention differs from each of these prior art briquets as set forth above in that the invented briquets have a density of from about 2.0 to 6.0 g/cc, and contain silica, carbon and a high percentage of iron, which is over 60% metallized, when the briquets are made by hot compaction. When the briquets are made by cold compaction, a binder such as sodium silicate or a mixture of calcium hydroxide and molasses is used.